Answers to Review Exercises

ASOS Pressure Alogrithm


Question 1

What is the difference in the number of barometers between a Class I site and a Class II site?

A. Class I site has 2 barometers and Class II site has 2 barometers
B. Class I site has 3 barometers and Class II site has 2 barometers
C. Class I site has 2 barometers and Class II site has 3 barometers
D. Class I site has 3 barometers and Class II site has 3 barometers

Your choice is ... incorrect

There is a difference in the number of barometers between Class I and Class II sites. Recheck the text and try again.

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Question 1

What is the difference in the number of barometers between a Class I site and a Class II site?

A. Class I site has 2 barometers and Class II site has 2 barometers
B. Class I site has 3 barometers and Class II site has 2 barometers
C. Class I site has 2 barometers and Class II site has 3 barometers
D. Class I site has 3 barometers and Class II site has 3 barometers

Your choice is ... incorrect

You have it backwards, try again.

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Question 1

What is the difference in the number of barometers between a Class I site and a Class II site?

A. Class I site has 2 barometers and Class II site has 2 barometers
B. Class I site has 3 barometers and Class II site has 2 barometers
C. Class I site has 2 barometers and Class II site has 3 barometers
D. Class I site has 3 barometers and Class II site has 3 barometers


Congratulations ! Your choice is ... correct

That right, Class II sites have one more barometer than Class I sites.

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Question 1

What is the difference in the number of barometers between a Class I site and a Class II site?

A. Class I site has 2 barometers and Class II site has 2 barometers
B. Class I site has 3 barometers and Class II site has 2 barometers
C. Class I site has 2 barometers and Class II site has 3 barometers
D. Class I site has 3 barometers and Class II site has 3 barometers

Your choice is ... incorrect

There is a difference in the number of barometers between Class I and Class II sites. Recheck the text and try again.

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Question 2

Where do you typically find the ASOS barometer?

A. Inside the ACU
B. Near the DCP
C. Mounted on a wall in a building
D. Moutned on a 10 foot pedestal next to the LEDWI


Congratulations ! Your choice is ... correct

Even though the ASOS barometers are inside the ACU inside a building, they are vented to the outside to ensure that they measure ambient pressure.

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Question 2

Where do you typically find the ASOS barometer?

A. Inside the ACU
B. Near the DCP
C. Mounted on a wall in a building
D. Moutned on a 10 foot pedestal next to the LEDWI

Your choice is ... incorrect

Sorry, the barometers are not located near the data collection platform (DCP) with most of the ASOS equipment.

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Question 2

Where do you typically find the ASOS barometer?

A. Inside the ACU
B. Near the DCP
C. Mounted on a wall in a building
D. Moutned on a 10 foot pedestal next to the LEDWI

Your choice is ... incorrect

The old mercury barometers were mounted on a wall, but ASOS has changed this practive. Please try again.

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Question 2

Where do you typically find the ASOS barometer?

A. Inside the ACU
B. Near the DCP
C. Mounted on a wall in a building
D. Moutned on a 10 foot pedestal next to the LEDWI

Your choice is ... incorrect

This location might be a nice place to put a barometer, but ASOS does not place it here.

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Question 3

How often do the ASOS pressure sensors sample data?

A. Once every 30 seconds
B. Once every second
C. Once every minute
D. Once every 10 seconds

Your choice is ... incorrect

ASOS samples pressure more frequently than once every 30 seconds. Please try again.

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Question 3

How often do the ASOS pressure sensors sample data?

A. Once every 30 seconds
B. Once every second
C. Once every minute
D. Once every 10 seconds

Your choice is ... incorrect

Not quite this often. Please try again.

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Question 3

How often do the ASOS pressure sensors sample data?

A. Once every 30 seconds
B. Once every second
C. Once every minute
D. Once every 10 seconds

Your choice is ... incorrect

Once a minute to too infrequent. Try a shorter sampling period.

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Question 3

How often do the ASOS pressure sensors sample data?

A. Once every 30 seconds
B. Once every second
C. Once every minute
D. Once every 10 seconds


Congratulations ! Your choice is ... correct

Super! By sampling the pressure once every 10 seconds ASOS uses six samples to arrive at the average one-minute pressure value.

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Question 4

Once a pressure sensor samples data every 10 seconds for 1- minute, what does the algorithm do with this data?

A. Takes the lowest of the values for pressure output
B. Does a harmonic mean of the six values
C. Does a linear average of the six values
D. Takes the higher of the six values for pressure output

Your choice is ... incorrect

ASOS does use the lowest pressure value at some point in the algorithm process, but not here. Please try again.

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Question 4

Once a pressure sensor samples data every 10 seconds for 1- minute, what does the algorithm do with this data?

A. Takes the lowest of the values for pressure output
B. Does a harmonic mean of the six values
C. Does a linear average of the six values
D. Takes the higher of the six values for pressure output

Your choice is ... incorrect

ASOS uses a harmonic mean in the visibility algorithm but not in the pressure algorithm. Sorry, please try another response.

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Question 4

Once a pressure sensor samples data every 10 seconds for 1- minute, what does the algorithm do with this data?

A. Takes the lowest of the values for pressure output
B. Does a harmonic mean of the six values
C. Does a linear average of the six values
D. Takes the higher of the six values for pressure output


Congratulations ! Your choice is ... correct

Nice job! This is the way that the pressure algorithm processes the six values from one pressure sensor.

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Question 4

Once a pressure sensor samples data every 10 seconds for 1- minute, what does the algorithm do with this data?

A. Takes the lowest of the values for pressure output
B. Does a harmonic mean of the six values
C. Does a linear average of the six values
D. Takes the higher of the six values for pressure output

Your choice is ... incorrect

Sorry, try again.

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Question 5

In a Class II system where you have 3 barometers to compare, if the 1-minute average pressure from all three barometers agree within 0.04 inch of mercury, what will be the output pressure value?

A. Value from barometer 1
B. Lowest value of the three 1-minute averages
C. Value from barometer 3
D. Average pressure value from all 3 barometers

Your choice is ... incorrect

The value from one barometer is used as the output pressure value, but not necessarily from barometer 1. Please try again.

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Question 5

In a Class II system where you have 3 barometers to compare, if the 1-minute average pressure from all three barometers agree within 0.04 inch of mercury, what will be the output pressure value?

A. Value from barometer 1
B. Lowest value of the three 1-minute averages
C. Value from barometer 3
D. Average pressure value from all 3 barometers


Congratulations ! Your choice is ... correct

Great choice! The lowest value is used to ensure that the other pressure values, such as altimeter setting, are in line with aviation requirements.

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Question 5

In a Class II system where you have 3 barometers to compare, if the 1-minute average pressure from all three barometers agree within 0.04 inch of mercury, what will be the output pressure value?

A. Value from barometer 1
B. Lowest value of the three 1-minute averages
C. Value from barometer 3
D. Average pressure value from all 3 barometers

Your choice is ... incorrect

The value from one barometer is used as the output pressure value, but not necessarily from barometer 3. Please try again.

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Question 5

In a Class II system where you have 3 barometers to compare, if the 1-minute average pressure from all three barometers agree within 0.04 inch of mercury, what will be the output pressure value?

A. Value from barometer 1
B. Lowest value of the three 1-minute averages
C. Value from barometer 3
D. Average pressure value from all 3 barometers

Your choice is ... incorrect

Averaging is limited to the individual sensors, but is not done among the three sensors. Please try again.

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Question 6

In computing field pressure, pressure sensor elevation and field elevation must be used in a formula along with what other weather parameter?

A. Temperature in degrees Rankine
B. Wind speed
C. Dewpoint
D. Density altitude


Congratulations ! Your choice is ... correct

Very good! Temperature is the parameter.

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Question 6

In computing field pressure, pressure sensor elevation and field elevation must be used in a formula along with what other weather parameter?

A. Temperature in degrees Rankine
B. Wind speed
C. Dewpoint
D. Density altitude

Your choice is ... incorrect

Sorry, wind speed is not used in any of the pressure calcuations. Please review the formulae and try again.

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Question 6

In computing field pressure, pressure sensor elevation and field elevation must be used in a formula along with what other weather parameter?

A. Temperature in degrees Rankine
B. Wind speed
C. Dewpoint
D. Density altitude

Your choice is ... incorrect

Sorry, dewpoint is not used in any of the pressure calcuations. Please review the formulae and try again.

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Question 6

In computing field pressure, pressure sensor elevation and field elevation must be used in a formula along with what other weather parameter?

A. Temperature in degrees Rankine
B. Wind speed
C. Dewpoint
D. Density altitude

Your choice is ... incorrect

Density altitude is a pressure parameters, and it not used in calculating field pressure. Please try again.

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Question 7

How often does the system check criteria for issuance of pressure remarks?

A. Once each second
B. Once each hour
C. Once each minute
D. Once each ten seconds

Your choice is ... incorrect

This is much too frequent. Remarks are required only for complete observations. Think about that and try again.

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Question 7

How often does the system check criteria for issuance of pressure remarks?

A. Once each second
B. Once each hour
C. Once each minute
D. Once each ten seconds

Your choice is ... incorrect

The hourly observations do require pressure remarks, but criteria are checked more often by ASOS. Please review the section on remarks and try again.

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Question 7

How often does the system check criteria for issuance of pressure remarks?

A. Once each second
B. Once each hour
C. Once each minute
D. Once each ten seconds


Congratulations ! Your choice is ... correct

Yes, ASOS does check for pressure remarks once each minute. These remarks, if present, become part of the complete observation produced every minute by ASOS.

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Question 7

How often does the system check criteria for issuance of pressure remarks?

A. Once each second
B. Once each hour
C. Once each minute
D. Once each ten seconds

Your choice is ... incorrect

Ten second samples are taken by the pressure sensor, but remarks are not made at this frequency. Please try again.

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Question 8

In generating a pressure change and tendency remark, the algorithm compares the current station pressure to the station pressure reported each hour for how many hours?

A. 1
B. 3
C. 6
D. 12

Your choice is ... incorrect

Sorry, what is the traditional length of time over which pressure change and tendencies are measured? Please try again.

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Question 8

In generating a pressure change and tendency remark, the algorithm compares the current station pressure to the station pressure reported each hour for how many hours?

A. 1
B. 3
C. 6
D. 12


Congratulations ! Your choice is ... correct

Yes, three hours is the standard pressure change measurement interval.

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Question 8

In generating a pressure change and tendency remark, the algorithm compares the current station pressure to the station pressure reported each hour for how many hours?

A. 1
B. 3
C. 6
D. 12

Your choice is ... incorrect

Sorry, too long an interval. Please review the section on pressure remarks and try again.

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Question 8

In generating a pressure change and tendency remark, the algorithm compares the current station pressure to the station pressure reported each hour for how many hours?

A. 1
B. 3
C. 6
D. 12

Your choice is ... incorrect

Upper air height changes are done at 12 hour intervals, but not surface pressure. Please review the text and try again.

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